Pressure vessels are commonly used for containing a variety of fluids under pressure, such as storing oxygen, natural gas, nitrogen, propane and other fuels, for example. Suitable container materials include laminated layers of wound fiberglass filaments or other synthetic filaments bonded together by a thermal-setting or thermoplastic resin. An elastomeric or other non-metal resilient liner or bladder often is disposed within the composite shell to seal the vessel and prevent internal fluids from contacting the composite material. The composite construction of the vessels provides numerous advantages such as lightness in weight and resistance to corrosion, fatigue and catastrophic failure. These attributes are due to the high specific strengths of the reinforcing fibers or filaments that are typically oriented in the direction of the principal forces in the construction of the pressure vessels.
FIGS. 1 and 2 illustrate an elongated pressure vessel 10, such as that disclosed in U.S. Pat. No. 5,476,189, which is hereby incorporated by reference. Vessel 10 has a main body section 12 with end sections 14. A boss 16 is provided at one or both ends of the vessel 10 to provide a port for communicating with the interior of the vessel 10. The vessel 10 is formed from an inner polymer liner 20 covered by an outer composite shell 18. In this case, “composite” means a fiber reinforced resin matrix material, such as a filament wound or laminated structure.
The liner 20 has a generally hemispheroidal end section 22 with an opening 24 aligned within an opening 26 in the outer composite shell 18. Boss 16 is positioned within the aligned openings and includes a neck portion 28 and a radially outwardly projecting flange portion 30. The boss 16 defines a port 32 through which fluid at high pressure may be communicated with the interior of the pressure vessel 10.
Liner 20 includes a dual layer lip circumscribing opening 24 in the liner 20, with an outer lip segment 34 and an inner lip segment 36 defining an annular recess 38 therebetween for receiving flange portion 30 of boss 16. Dovetailed inter-engaging locking means 40 are provided between flange portion 30 and outer and inner lip segments 34 and 36, respectively, to lock liner 20 to boss 16.
This type of interlocking liner and boss structure has proved effective in certain applications, such as for compressed natural gas (CNG) fuel containers. However, in high pressure (e.g., 700 bar) service, distortions of the plastic liner material adjacent the boss has been noted, leading to some tendency of the plastic to be pulled out of the keyway (i.e., out of the interlocking means 40). The “distortion” of this area in high pressure applications comes from the presence of high pressure gas in the keyway between the liner 20 and boss 16. High pressure gas saturates the liner material and then outgases when the pressure drops. Thus, the gas permeating the area between the liner 20 and boss 16 can then have a higher pressure than the gas within vessel 10, such as, for example, when gas is being vented from the vessel 10. As a result, the excess pressure between the liner 20 and boss 16 can cause the liner material to be forced out of the keyway. Thus, there remains a need for a liner and boss interface structure that prevents separation of the liner and boss under high pressure and that allows venting of any such gas trapped in the keyway between the liner and the boss.